1. Field of the Invention
The present invention relates to a dye-containing curable composition that is suitable for forming a colored image in a color filter used in liquid crystal displays or solid-state image elements, as well as to a color filter prepared using the composition, and to a process of preparing the color filter.
2. Description of the Related Art
As a method of preparing a color filter for use in liquid crystal displays or solid-state image elements, a dyeing process, a printing process, an electrodepositing process and a pigment dispersing process are known.
The dyeing process comprises dyeing a substrate, that is made of a natural resin (e.g., gelatin, glue and casein) or a synthetic resin (e.g., amine-modified polyvinyl alcohol), with a dye such as an acid dye, to thereby prepare a color filter.
The dyeing process involves problems with respect to lightfastness, heat resistance and humidity resistance due to using the dye, a problem in that color unevenness occurs when producing large size screens because it is difficult to uniformly control dyeing and fixing characteristics, and a problem in that a procedure is complicated since an anti-dyeing layer is needed when conducting the dyeing.
The electrodepositing process comprises forming transparent electrodes in a prescribed pattern beforehand, ionizing a resin that contains a pigment dissolved or dispersed in a solvent, and applying a voltage to form a colored image in accordance with a pattern shape, to thereby prepare a color filter.
This electrodepositing process requires a photolithographic step including film-forming and etching steps for producing transparent electrodes for forming a color filter in addition to transparent electrodes for display. During this process, if a short circuit occurs, line defects are generated leading to a reduction in yield. In principle, this process is difficult to apply to alignments other than a stripe alignment, such as a mosaic alignment. Moreover, this process has a problem in that control of the transparent electrodes is difficult.
The printing process is a simple and easy process for preparing a color filter, in which an ink that contains a thermosetting resin or a ultraviolet-curing resin and a pigment dispersed therein is used for printing, such as offset printing. However, because of a high viscosity of the ink used in this process, filtering is difficult, and defects resulting from contaminants, foreign matter or gelling of an ink binder are easily generated. Further, this process involves problems with respect to position precision, line width precision, and plane smoothness depending on printing precision.
The pigment dispersing process is a process employed for preparing a color filter, through a photographic technique using a colored radioactive composition containing a pigment dispersed in various photosensitive compositions. Since this process uses pigments, it is stable against light and heat. Further, since patterning is carried out by the photolithographic technique, the pigment dispersing process is suitable for the preparation of a color filter that achieves a sufficient position precision and is suitable for use in large-size screens and high resolution color displays.
In order to prepare a color filter by the pigment dispersing process, a radioactive composition is applied on a glass substrate using a spin coater, a roll coater or the like, followed by drying to form a coated film, which is then subjected to pattern exposure and development to thereby form colored pixels. This procedure is carried out for respective colors to obtain the color filter.
For use in the pigment dispersing process, negative-type photosensitive compositions have been disclosed which comprise a photopolymerizable monomer, a photopolymerization initiator and an alkali-soluble resin (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 1-102469, 1-152499, 2-181704, 2-199403, 4-76062, 5-273411, 6-184482 and 7-140654).
However, in recent years, a still higher resolution is being demanded for color filters used in solid-state image elements. But, by employing the conventional pigment dispersing system, resolution cannot be enhanced, and color unevenness occurs due to coarse particles of the pigment. Accordingly, the pigment dispersing process is not suitable for the applications that require fine patterns, such as for use in solid-state image elements. In order to solve this problem, use of a dye has been proposed (see, for example, JP-A No. 6-75375).
Dye-containing curable compositions involve the following newly raised problems (1) to (4):    (1) Since conventional dyes are low in solubility in an alkaline aqueous solution or an organic solvent, it is difficult to obtain a liquid curable composition having a desired spectrum.    (2) Since dyes often interact with other components in a curable composition, it is difficult to regulate solubility (developability) at cured portions and non-cured portions.    (3) In a case where a molar absorptive coefficient (F) of a dye is low, addition of a large amount of the dye is required. For this reason, an amount of other components in the curable composition, such as polymerizable compounds (monomers), binders and photopolymerization initiators must be reduced, thereby raising other problems such as lowered curability and reduced heat resistance of the composition after curing, and impaired developability at cured portions and non-cured portions.    (4) Generally, dyes are inferior to pigments in lightfastness and heat resistance.
Owing to the aforementioned problems, it has been difficult to achieve a fine colored pattern for high resolution thin color filters.
Further, in contrast to when applied for preparation of semi-conductors, when applied for preparing color filters for solid-state image elements, the composition is required to have a film thickness of 1 μm or less. Accordingly, in order to exhibit a desired absorption, a large amount of the dye must be added to the curable composition, which results in occurrence of the foregoing problems.
On the other hand, there are known dyes that contain salts with various amines having enhanced solubility with respect to acid dyes. Examples thereof include amine salts of “Acid Yellow 42” having solubility in alkaline aqueous solutions or organic solvents (e.g., ditolylguanidine salts). However, since these amine salts do not have an OH group in their imine moiety, interaction with other components present in a resist considerably lowers their alkaline developability. Further, since an azo-based acid dye represented by “Acid Yellow 42” can take various conformations, a molar absorptive coefficient thereof may occasionally be lowered. Accordingly, when these amine salts have counter ions having a high molecular weight, a color value (absorbance/weight) decreases, and hence a large amount of the dye must still be added to the resist composition. For this reason, problems similar to those described above arise, and therefore, improvements have been demanded (see, for example, JP-A No. 59-30509).